I use both options and when you can afford it, it really shouldn't be a matter of exclusion but more a matter of finding the right tool for the right situation.
When recording I usually use the Kemper, but I almost exclusively use profiles I made of my own amps which I have known of years and have learned where their sweet spots are. It's indistinguishable from using the real thing to be honest. I have a professional recording studio and I usually had the amp head in the control room and the cabinet miked up in the live room so I took the "amp in the room feel" out of the equation when comparing to the KPA, and there really is no significant difference.
However I do use the UA OX from time to time especially when I know the gig requires me fiddling around with amp settings, for instance between songs. On the other hand, I have profiled most of the settings that I used during these specific sessions so I use the OX less and less. I keep it around in the studio for when a client wants to use his real amp without making too much noise.
The thing I personally love about the Kemper when compared to using tube amps is its stability, reliability, consistency and ergonomics. No more worrying about tube replacement or cap replacement in old amps etc. No more hauling both the Plexi head and the Dumble clone head to gigs etc. That's what really stands out for me.
The one thing I would advise you is: profile, profile, profile. The Kemper can store so many profiles, just make one every time you find a useful sound, it really takes a matter of minutes. And document everything, not just in Rig Manager, but in a separate document. Also, try making a profile of your amp connected to for instance the UA OX, this will give great results as well and makes it able to profile in silence.
